The phrase "old bulbs" refers to traditional light bulbs that were commonly used in the past, before newer, more energy-efficient options became available. Full definition
Open curtains and blinds as much as possible and swap old bulbs for full - spectrum light to see colors pop to life and moods lift almost instantly. (mindbodygreen.com)
Old bulbs lose up to 50 per cent of their brightness over time, but because it's a gradual degradation this is not always noticed. (educationbusinessuk.net)
It would be great if you could post up pictures of the new and old bulbs also. (mechanics.stackexchange.com)